This invention relates generally to a composition for controlling the release of microbicidally active compounds. In particular, this invention relates to the use of metal oxide glasses to control the release of microbicidally active compounds.
The ability to control release of biologically active compounds to a locus to be protected is important in the field of microbicidally active compounds. Typically, when a microbicidally active compound is added to a locus to be protected, the compound is rapidly released, whether or not it is needed. Controlled release compositions deliver the biologically active compound in a manner that more closely matches the need for the compound. In this way, only the amount of the biologically active compound needed is released into the locus to be protected. Controlled release offers the advantages of reduced cost, lowered toxicity and increased efficiency.
Various methods of controlled release are known. Such methods include encapsulation of the microbicidally active compound, adsorption of the microbicidally active compound on an inert carrier, such as silica gel, and clathration of the microbicidally active compound.
All of these methods have drawbacks to widespread commercial use, such as expensive starting materials, limited compatibility of the controlled release method to the compounds to be released or locus to be protected, and limited control of the release of the microbicidally active compounds. For example, adsorption of a microbicide on an inert carrier results in a composition that releases the microbicide in a diffusion controlled manner. Such compositions usually do not provide control of the release of the microbicide. Additionally, whether a clathrate forms or not depends on the solvent used, which limits available solvent choices.
U.S. Pat. No. 5,591,453 (Ducheyne et al.) discloses biologically active molecules in a silica based glass to provide controlled release of the biologically active molecules. The biologically active molecules disclosed are all pharmaceutical agents, such as drugs and growth factors. This patent is directed to using these glasses in the acceleration and regeneration of bone tissue and a reduction in the incidence of infection in the area adjacent to the glasses when implanted in a person. There is no discussion of incorporating non-pharmaceutical agents, such as microbicides or agricultural pesticides, into the glasses. This patent teaches that the release of the biologically active molecules is controlled by varying the size of the glass particles from 500 microns to 5 millimeters. Increasing the particle size slows down the release of the biologically active molecules because it takes longer for the biologically active molecule to diffuse out of the particle. This is an inefficient method to control the release of biologically active molecules. Also, the large particle sizes required to slow the release of the biologically active molecules are incompatible with most industrial systems, such as coatings and paints. Large particles, when added to a paint, adversely affect the gloss.
Japanese patent application 07 291 805 A (Yamamoto) discloses agricultural pesticides incorporated into metal oxide glasses prepared from metal alkoxide monomers. The metal alkoxide monomers contain only alkoxy groups. This patent application does not teach modification of the metal oxide glass in order to vary the release rate of the incorporated agricultural pesticide.
There is therefore a continuing need for controlled release compositions of biologically active compounds, such as microbicides, marine antifouling agents and agricultural pesticides, that are inexpensive, compatible in a broad range of loci to be protected, have a small particle size, and more efficient at controlling the release of the biologically active compound than compositions currently available.